<===> input.scss
@mixin media($var1, $var2) {
  @media screen and ($var1: $var2) {
    @content;
  }
}

@include media(max-device-width, 500px) {
  foo {
    bar: "works";
  }
}
<===> output.css
@media screen and (max-device-width: 500px) {
  foo {
    bar: "works";
  }
}